Field
The disclosed technology generally relates to magnetic devices, and more particularly to spin torque devices.
Description of the Related Technology
In the so-called “post Moore era,” spintronics devices or spin torque devices have become increasingly popular because they can potentially offer new and improved characteristics over traditional devices such as transistor-based devices, making such devices promising candidates for future logic and memory applications.
In general, the operation of spin torque devices is based on a phenomenon known as spin transfer torque. According to this phenomenon, when a current is passed through a magnetization layer having a fixed magnetization, sometimes referred to as a fixed layer, the resulting current can become spin polarized. In other words, a majority of the electrons passing through the magnetization layer possess the same spin and are oriented, e.g., in the same direction of magnetization as that of the fixed layer. Such electrons are referred to as spin-polarized electrons.
When the spin-polarized electrons pass through one or more non ferromagnetic layers, such as a tunnelling layer, and injected into a subsequent magnetic layer, the spin of the spin-polarized electrons can transfer a spin torque to the magnetization of the subsequent magnetic layer. The subsequent magnetic layer is generally referred to as a free layer. The transfer of the spin torque to the magnetization of the free layer can result in a change, e.g., a switching, in the magnetization orientation of the free layer.
When the current the current passing through the free layer exceeds a certain critical value, the magnetization of the free layer may be switched. The magnitude of the critical current is determined by many factors, including the materials and dimensions of the layers of the stack (sometimes referred to as the magnetic tunnelling junction (MTJ)), which can include the fixed layer, the free layer and the tunneling layer as described above, as well as its surroundings.
However, the magnetization of the fixed layer may still remain unchanged since the current used may not be strong enough to affect the magnetization of the fixed layer although being sufficient to switch the magnetization of the free layer.
Generally the state of the free layer may be read out by measuring the magneto-resistance of the free layer.
A type of spin torque device is a spin torque majority gate. A spin torque majority gate is a logic device whose output depends on the majority of its multiple inputs. A spin torque majority gate and a method for manufacturing the device are disclosed in WO 2011/075257 A2. The described spin torque majority gate aims at setting the magnetization of the free layer based on the majority of inputs. However, to realize such an effect has proven hard since e.g. the magnetization of the free layer is not reliably set resulting in that readout of the device is difficult or even impossible. The difficulties of reading out may for instance relate to undesired domain walls being formed within the free layer, restraining the magnetization of the free layer in an unfavourable manner, setting a wrong magnetization state after writing operation.
Hence, there is a need for an improved spin torque majority gate device.